The invention relates to monolithic integrated circuits fabricated on low loss, high resistivity ceramic substrates.
The invention arose during continuing development efforts directed toward manufacturing advanced and cost effective microwave, millimeter and electro-optic monolithic integrated circuits (MMICs) capable of high temperature operation. A new approach adapts a low loss, high resistivity ceramic substrate onto which is grown high resistivity semi-insulating buffer layer to transitionally achieve lattice match to a compound semiconductor's lattice, and enable growth of single crystalline epitaxial layers to fabricate the MMICs.
The ability to grow active layer single crystal compound semiconductors, such as GaAs, GaAlAs, InGaAs, Si and InP, and to develop a transitional buffer layer to achieve lattice match enables a totally new approach to the development and methods of fabricating MMICs capable of highest performance and reliability, and for operation in the microwave to optical wavelength region.
In a further embodiment, selected buffer layers enable growth of high temperature superconductors (HTS) on the same ceramic substrate, in addition to the above noted active layer. Active components such as FETs, MESFETs, diodes, HEMTs (high electron mobility transistors) and the like are fabricated in the active layer. Passive components such as low loss passive networks, filters, delay lines, capacitors, resistors, etc. are fabricated in the HTS layer.
In a further embodiment, electro-optical devices are fabricated on the same substrate. The ability to use a ceramic substrate having a low loss tangent and which is optically transmissive, facilitates the fabrication of electro-optical transmitters and receivers.
In a further embodiment, the epitaxial growth on the ceramic substrate eliminates a semi-insulating layer otherwise discretely bonded on the substrate and subject to fracture problems due to mechanical stresses caused by mismatch of thermal expansion coefficients. The invention improves reliability and minimizes the noted fracture problems by eliminating the discrete bonding of the semi-insulating layer to the ceramic substrate and by eliminating the semi-insulating layer, which also improves thermal conductivity of an MMIC by eliminating the poor thermal conductivity semi-insulating layer. The invention also enables hermetic sealing of the MMIC by direct eutectic bonding of a metal cover to the ceramic substrate.